There are a variety of apparatus available for styling hair. One form of apparatus is known as a straightener which employs plates that are heatable. To style, hair is clamped between the plates and heated above a transition temperature where it becomes mouldable. Depending on the type, thickness, condition and quantity of hair, the transition temperature may be in the range of 160-200° C.
A hair styling appliance can be employed to straighten, curl and/or crimp hair.
A hair styling appliance for straightening hair is commonly referred to as a “straightening iron” or “hair straightener”. FIG. 1 depicts an example of a typical hair straightener 1. The hair straightener 1 includes first and second arms each comprising an arm member 4a, 4b and heatable plates 6a, 6b coupled to heaters (not shown) in thermal contact with the heatable plates. The heatable plates are substantially flat and are arranged on the inside surfaces of the arms in an opposing formation. During the straightening process, hair is clamped between the hot heatable plates and then pulled under tension through the plates so as to mould it into a straightened form. The hair straightener may also be used to curl hair by rotating the hair straightener 180° towards the head prior to pulling the hair through the hot heatable plates.
A hair styling appliance for crimping hair is commonly referred to as a “crimping iron”. FIG. 2 depicts an example of a typical crimping iron 10). The crimping iron includes first and second arms. Each arm comprises an arm member 14a, 14b and heatable plates 16a, 16b coupled to heaters (not shown) in thermal contact with the heatable plates. The heating plates have a saw tooth (corrugated, ribbed) surface and are arranged on the inside surfaces of the arms in an opposing formation. During the crimping process, the hair is clamped between the hot heatable plates until it is moulded into a crimped shape.
Ceramic heaters, in particular those with a pure resistive profile enable optimisation of the thermal control loop, thus allowing the plates in contact with hair to remain near transition temperature during styling and thermal load application. This leads to longevity of style.
Conventional ceramic heaters typically comprise a layered structure having an electrical heater element sandwiched between two layers of ceramic/embedded within the ceramic plate. A heatable plate is then thermally coupled to the heater, on one side of the heater/ceramic sandwich, which provides a contact surface for styling hair.
One problem of heating ceramic used in such heaters is that they can bend as they heat due to differential thermal expansion (sometimes referred to as a ‘banana’ effect owing to a curving of the plate). Tiny fissures and cracks in the ceramic structures mean that over time, the ceramic may crack, leading to a reduced lifetime of the product. The sandwiching arrangement (with the heater element embedded in the ceramic) goes some way to overcoming this problem, forming a ‘balanced heater’. As each ceramic layer is heated by the central heating element, bending under the effect is minimised as the structure is held in a straightened form as the ceramic either side of the heater element oppose one another as they attempt to bend under heating.
However, one downside of this approach is that it requires ceramic heaters to be manufactured with the heater element layer embedded. Furthermore, use of an embedded heater means a surface mount thermistor cannot be used on the heater to measure temperature of the heater accurately—by sitting on the ceramic upper layer, the thermistor would be thermally less well coupled. In addition, provision of more ceramic means the overall thermal mass is increased.
The applicant has recognised a need to improve existing hair styling appliances to address such matters.